1. Field of the Invention
The present invention pertains to a method for forming a composite sole to an upper of a shoe. More particularly, the present invention pertains to a method of molding a blank midsole to an upper of a shoe while protecting the material of the upper from the heat involved in molding the midsole to the upper, and subsequently adhering an outsole having a desired traction surface to the blank midsole.
2. Description of the Related Art
Prior art methods of constructing footwear entirely of rubber include a method where a rubber midsole is formed unitarily with a rubber upper by vulcanization, and following vulcanization of the midsole and upper an outsole is separately secured to the midsole. An example of the above described prior art method of constructing rubber footwear is disclosed in U.S. Pat. No. 4,703,533.
The above described prior art method of constructing rubber footwear cannot be employed in constructing footwear where only the sole is constructed of rubber and the upper is constructed of some other flexible material, for example leather, because the leather of the upper would be damaged by the heat of the vulcanization process. However, prior art methods are known of forming an entire shoe sole to an upper constructed of a flexible material, for example leather, without subjecting the entire upper to the heat associated with the sole forming process. According to this known method of construction, the upper is first formed with a welt sewn to a periphery of the bottommost edge of the upper. The upper and sewn welt are then fitted on a conventional last with an outer peripheral edge of the welt and the bottom peripheral portion of the upper to which the welt is sewn positioned over the periphery of the last sole forming surface. A ring mold is next attached around the last with the welt being fitted into a groove formed in the ring mold, thereby positioning an inner peripheral edge of the welt and the bottom periphery of the upper to which the welt is sewn over the sole forming surface of the last.
An insole, frequently constructed of a piece of fiberboard dimensioned to the configuration of the upper interior defined by the welt, is next inserted into the ring mold and positioned on the sole forming surface of the last. When a shankpiece is constructed into the shoe sole according to this prior art method, it is frequently adhered to the bottom surface of the insole, which is the surface facing upwardly as the insole rests on the sole forming surface of the last within the ring mold.
One or more pieces of raw rubber are next inserted into the ring mold on top of the insole, and then a vulcanizing piston is moved downwardly into the ring mold. The piston compresses the pieces of rubber between the piston face and the insole resting on the sole forming surface of the last. The piston is then heated in a process that vulcanizes the pieces of rubber into a complete sole formed on the welt and upper mounted to the last. The piston face has a configuration specifically designed to mold a particular tread surface into the bottom of the sole as it is formed. As an example of one known vulcanizing process, the vulcanizing piston is heated to a temperature of 410.degree. F. and remains in its dwell position within the ring mold vulcanizing the rubber into a sole on the upper for a time period of 17 minutes in order to sufficiently cure the rubber.
When the vulcanizing time period has elapsed, the piston is removed from the ring mold and the ring mold is removed from around the shoe forming last. The completed shoe, having a complete sole formed to the welt stitched at the bottom periphery of the upper, is removed from the shoe forming last completing this prior art process.
This prior art method of forming a complete sole to the upper of footwear has been found to be disadvantaged in that it requires a specific set of molds for each size of the footwear being produced, and an additional multiple of molds for each size of footwear where the footwear is provided with varying tread surfaces on the footwear soles. For example, if it desired to manufacture the same piece of footwear of a specific size having various different types of tread surfaces such as slip resistant surfaces, wear resistant surfaces or electrostatic dissipating surfaces, the old method of forming a complete sole to the footwear would require a separate piston and likely a separate ring mold for each of the different tread surfaces in order to construct each of these different soles to the upper of footwear according to the old method. The costs involved in having these different pistons and molds for manufacturing footwear with differing soles contribute significantly to the overall costs of producing the footwear.